Origin Notes and History:

The crown colony of British Columbia was proclaimed 19 November 1858, bounded by USA, Rocky Mountains, Finlay and Nass Rivers, excluding Vancouver Island and all other islands south of 52º. The capital was Fort Langley, followed by New Westminster; governor James Douglas. On 28 July 1863 the boundary was extended to 60º latitude and 120º longitude. The Colony of Vancouver Island and the Colony of British Columbia were united 19 November 1866; capital, Victoria; governor Frederick Seymour. British Columbia joined the Dominion of Canada as a province 20 July 1871; premier John Foster McCreight; lieutenant governor Joseph W. Trutch.

Prior to settlement in 1846 of the boundary between British and United States territory west of the Rocky Mountains, most of present British Columbia was part of the jointly occupied Oregon Territory. Thereafter, 11 March 1859, the colony of Vancouver's Island was established. As the name "Oregon" was kept by the US territory, the British mainland was left without a name except "New Caledonia", the name given by the North West Company fur traders to the central interior when they came in by Peace River (first permanent settlement, Fort McLeod, 1805). This name was proposed when colonial government for the mainland was being planned, but was questioned and referred to Queen Victoria, who replied: "The Queen has received Sir E. Bulwer Lytton's letter. If the name of "New Caledonia" is objected to as being already borne by another colony or island claimed by the French, it may be better to give the new colony west of the Rocky Mountains another name. New Hanover, New Cornwall, and New Georgia appear from the maps to be the names of subdivisions of that country, but do not appear on all maps. The only name which is given to the whole territory in every map the Queen has consulted is "Columbia", but as there exists also a Columbia in South America, and the citizens of the United States call their country also Columbia, at least in poetry, "British Columbia" might be, in the Queen's opinion, the best name." (excerpt from 24 July 1858 letter to Sir Edward Bulwer-Lytton, Colonial Secretary)
See further discussion about the impetus to determine a name for the colony, and the relative merits and drawbacks of various suggestions in an article by Ged Martin, professor of modern history at University College, Cork, published in the British historical journal "Albion", reprinted in Victoria Times, 22 September 1979, p.22.

In 1792 Captain Robert Gray from Boston re-discovered the river which the Spaniards had named "Rio de San Roque" some 17 years earlier. Ignorant of the Spaniards' prior discovery, Gray named the great river after his ship, the Columbia. In the following years it was natural enough that the vast area drained by the Columbia River should be referred to increasingly as the Columbia country. When the Hudson's Bay Company set up two administrative areas west of the Rockies, they named the more northerly New Caledonia and the more southerly Columbia. After the Treaty of Washington in 1846 fixed the 49th parallel as the boundary, most of the old HBC Department of Columbia became American. Somebody was bound to think of using "British Columbia" as a name for what was left north of the new boundary line. The person who took this final step was Queen Victoria.